Filters

The API of action filters has been changed in DotVVM 1.1. See the Upgrading from DotVVM 1.0 page for more information.

In large apps and sites, you need to do apply global actions e.g. for each button click on a specific page, section or even on all pages in the app.

You might need to do global exception handling and logging, or you just need to check ModelState.IsValid on each postback.

In DotVVM, we have a concept of filters for this purpose. If you know Action Filters in ASP.NET MVC or ASP.NET Web API, it is the same concept.

Action Filters

If you want to apply a common logic to one or more viewmodels, viewmodel commands or a whole application, you have to create a class that derives from ActionFilterAttribute.

You have 4 methods you can override in this class:

• OnViewModelCreated - this method is called after the viewmodel was created. You can use it to set additional viewmodel properties.

• OnCommandExecuting - this method is called right before the method referenced in the command binding is invoked. This method is only invoked during the postback.

• OnCommandExecuted - this method is called right after the method referenced in the command binding was finished. This method is only invoked during the postback.

• OnResponseRendering - this method is called right before the viewmodel is serialized and the response is rendered.

Model Validation using Filters

If you want to perform the model validation before every command, it is not difficult. Actually, DotVVM already include such filter and registers it for all requests by default.

using System;
using System.Collections.Generic;
using System.Linq;
using DotVVM.Framework.Hosting;
using DotVVM.Framework.ViewModel;

namespace DotVVM.Framework.Runtime.Filters
{

    /// <summary>
    /// Runs the model validation and returns the errors if the viewModel is not valid.
    /// </summary>
    public class ModelValidationFilterAttribute : ActionFilterAttribute
    {

        private ViewModelValidator viewModelValidator = new ViewModelValidator();

        /// <summary>
        /// Called before the command is executed.
        /// </summary>
        protected internal override void OnCommandExecuting(IDotvvmRequestContext context, ActionInfo actionInfo)
        {
            if (!string.IsNullOrEmpty(context.ModelState.ValidationTargetPath))
            {
                // perform the validation
                context.ModelState.Errors.AddRange(viewModelValidator.ValidateViewModel(context.ModelState.ValidationTarget));

                // return the model state when error occurs
                context.FailOnInvalidModelState();
            }

            base.OnCommandExecuting(context, actionInfo);
        }
    }
}

In the OnCommandExecuting method we have to check whether the ValidationTargetPath is set or not. If not, then the validation was disabled on the control which fired the postback.

We need to perform the validation and call FailOnInvalidModelState, which throws an exception and return the model errors to the client, if there are any. If the viewmodel is valid, it doesn't do anything.

DotVVM serializes the validation errors and displays the validation errors in the page.